The 500-hPa circulation
pattern during July featured above-average heights over the southwestern
U.S.
, across the high latitudes and subtropical latitudes of the
North Atlantic
, and over the central North Pacific, and below-average heights over western
Canada
and the central
North Atlantic
(Figs. E9, E11).
The main surface temperature departures reflected above-average temperatures
across southern
Alaska
, the southwestern and eastern
U.S.
, most of
Europe
, both the high latitudes and subtropical latitudes of the
North Atlantic
, and much of
China
(Fig. E1). The main precipitation anomalies
during July included above-average totals from
Texas
to the Mid-Atlantic region of the
U.S.
, and the western subtropical
North Atlantic
, and below-average totals in portions of the mid-western
U.S.
and across the high latitudes of the
North Atlantic
(Figs. E3, E5, E6).

a. North America

The main 500-hPa circulation
anomalies affecting the North American sector during July were above-average
heights over both the southwestern and eastern
United States
, and below-average heights over western
Canada
/ eastern
Alaska
(Fig. E9). This anomaly pattern contributed
to enhanced precipitation across southern
Alaska
, with totals in many regions reaching the 90th percentile of
occurrences. It also contributed to well above-average temperatures in the
southwestern
U.S.
, which was situated beneath a very persistent upper-level ridge for most of
the month (Fig. E1).

The anomalous upper-level
cyclonic circulation over the middle of the
U.S.
(Fig. E10) contributed to well
above-average temperatures throughout the east (Fig. T21).
Enhanced rainfall was observed downstream of the trough axis from
Texas
northeastward to the Mid-Atlantic region, and significantly below-average
rainfall was observed in
Illinois
immediately upstream of the trough axis (Fig.E3).

Well above-average
precipitation was also observed across the
Gulf
Coast
region during July, in response to two landfalling tropical systems.
Tropical Storm Cindy made landfall on 6 July and brought 100 – 150 mm of
rain to the
Louisiana
and
Mississippi
coasts. Major Hurricane Dennis made landfall at
Pensacola
,
Florida
on 10 July, and brought more than 200 mm of rain to the western
Florida
panhandle, western
Alabama
, and western
Georgia
.

b.
North Atlantic

The 500-hPa circulation
pattern during July featured above-average heights across the high latitudes
and subtropical latitudes of the
North Atlantic
(Fig. E11). This pattern was associated
with a continuation of exceptionally warm SSTs throughout both regions, with
departures exceeding the 90th percentile in the subtropics (Figs.
T18, E1). This
anomaly pattern reflects the ongoing warm phase of the Atlantic
multi-decadal mode that began approximately in 1995 (Goldenberg et al. Science,
2001).

These
conditions were again associated with above-average temperatures across most
of
Europe
, with departures in most areas exceeding the 70th percentile of
occurrences. In the subtropics the anomalous warmth and amplified
upper-level ridge (Fig. T22) were also
associated with significant Atlantic tropical storm and major hurricane
activity during the month. By the end of July, a record seven tropical
storms and two major hurricanes had formed in the
Atlantic
Basin
. This tropical activity was associated with a known set of conditions that
favors tropical cyclogenesis. These conditions include 1) lower surface air
pressure (Fig. T19) across the tropical
Atlantic and Caribbean Sea, and 2) markedly reduced vertical wind shear over
the tropical North Atlantic and Caribbean Sea, in response to a combination
of anomalous easterlies at 200-hPa and weaker-than-average tropical easterly
trade winds at 850-hPa (Figs. T20, T21).

2. Southern Hemisphere

In the middle latitudes, the mean 500-hPa circulation
pattern during July featured an anomalous zonal wave 3-4 pattern, with
persistent above-average heights in the vicinity of the three continents,
and a more variable pattern of below-average heights over portions of the
three ocean basins (Fig. E15). At lower
latitudes, the 200-ha subtropical ridges were stronger than average
throughout the Southern Hemisphere, with the largest anticyclonic anomalies
occurring between
Africa
and
Australia
(Fig. T22). This anomaly pattern was
associated with enhanced upper-level westerlies and a nearly uniform South
Pacific jet stream from the central
Indian Ocean
to southern
South America(Fig. T21).

In
Australia
, above-average temperatures and below-average precipitation resulted from
the combination of a persistent upper-level ridge across the southern part
of the continent and an associated poleward shift of the mean jet stream.
The most significant precipitation deficits were observed in the southwest,
where totals were generally in the lowest 10th percentile of
occurrences.

The persistent pattern of above-average heights over
southern
Africa
contributed to well above-average temperatures during the month.
Temperatures over much of
South Africa
were 1°-2°C above average, with many areas recording values exceeding the
90th percentile of occurrences.